Dashn is a Korean go server with an English interface.
The common belief is that this is the place to play fighting games.
Interesting Features:
User Experiences:
DashnUserExperiences, DashnStyle
FAQ: DashnFAQ
Registration:
http://english.dashn.com/newcommers/registration.htm
Microsoft Windows-only client download: http://english.dashn.com/download/download.htm
(Linux and wine works for some people, not for others; see DashnFAQ)
Professional teachers.